Conventionally, a path switching system for protecting a network against an error has been that, when a path error is detected by some means and only when an error alarm occurs, each path is switched in the event-driven manner independently--that is, without assigning recovery priority to paths or establishing an inter-path relationship.
For example, Japanese Patent Kokai Publication JP-A No. 4-96477 (Title of invention; Virtual path switching apparatus) discloses a path search system for use when a plurality of errors occur in a virtual path. A system described in this disclosure adds to a recovery control signal two types of information, that is, an identification number identifying a link where an error occurred and error recovery priority information indicating which of a plurality of errors is to be recovered with priority; the system then determines recovery priority, and creates bypass circuits, step by step. To do so, the system has recovery status recording means which keeps in storage several kinds of information: error recovery involvement information indicating whether a local communication node is connected to a failed link or the node is used for linking a bypass path, recovery progress status information indicating error recovery progress status, and determined priority information indicating which of a plurality of recovery control signals is to be processed with priority.
Recovery priority processing means adds to a recovery control signal on the other hand, a number identifying a failed link or communication node which was determined as failed when cut-off of a virtual path with an up-stream communication node was detected, and on the other hand adds the recovery priority information. When a plurality of recovery control signals were generated due to occurrence of a plurality of errors, the means determines the recovery priority based on the recovery priority information and establishes bypass circuits, step by step.